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The invention relates to aircraft collision avoidance systems and, more particularly, to such systems able to provide collision avoidance and evasive action alerts to pilots of fixed wing and other aircraft operating in close proximity, independently of reliance on Global Positioning System (GPS) inputs.
A typical prior type of aircraft collision avoidance system (CAS) may be designed for use by aircraft flying on independent flight paths, such that the aircraft are normally relatively widely separated. A collision risk may arise because, while basically proceeding on disparate flight paths, at some point in time the two aircraft may begin to approach each other unexpectedly. Thus, the intention may be that one aircraft should not come into close proximity to another and a CAS may be designed to give warning to avoid having a close proximity situation arise. For this purpose, a close proximity situation may be considered to arise when two aircraft are within one mile range and one thousand feet vertical separation of each other, or closer.
A wide variety of CAS approaches have previously been proposed, many to address the situation just described. Typically, the two aircraft which become exposed to a close proximity situation have no prior relationship to each other and each was unaware of the intended flight path of the other aircraft. The problem may commonly arise because of an unintended flight path, as where one aircraft unknowingly deviates toward or into an unauthorized altitude or flight path. A common aspect of collision avoidance in such circumstances is that the relevant aircraft are not intended to come within close proximity of each other and the objective is to maintain relatively large aircraft separations in range and altitude. To meet such collision avoidance objectives, prior systems may employ radar, communication, or GPS techniques, or combinations thereof, which are particularly suited to monitoring and detection of the potential for close proximity situations.
A qualitatively different situation exists when aircraft are intentionally placed in a close proximity situation. For example, a group of aircraft may be positioned in a relatively close formation in the course of a flight for military or other purposes. Fixed wing, helicopters and other aircraft of the same or mixed types may also be called upon to operate in relatively close proximity in the course of efforts on common or related projects or missions. In such situations, intended aircraft separations may be as small as one hundred feet vertically and laterally, or less. Prior CAS systems have generally been unsuitable for providing reliable collision avoidance performance under conditions of such small intended separations between aircraft. The basic system parameters may be inapplicable to close aircraft operations and some prior systems may also be limited as to suitable performance where both fixed and rotary wing aircraft are involved. System reliance on GPS data may also limit close formation capabilities of prior system approaches. Thus, with reliance on GPS data, overall system accuracy or potential interruptions in data availability may be unacceptable in the context of close tolerances and quick continuous response characteristics required in close formation operation.
Objects of the present invention are, therefore, to provide new and improved collision avoidance systems, and such systems having one or more of the following characteristics and capabilities;
continuous monitoring of separations and rate of closure between aircraft in close formation or proximity;
direct measurement of range and closing rate based on signal transit time between aircraft;
operable for fixed-wing aircraft at high speed formation flight or dynamic maneuvering;
operable for helicopters operating at separations of two to three rotor diameters;
operable independently of, or supplemented by, GPS data;
mutual ranging and positioning based on signals transmitted by each aircraft;
low power, short range operation;
low probability of detection and interception;
local radio sub-net, with participation by small number of aircraft in a common neighborhood;
continuous position monitoring with critical situation alarms or recommended evasive action alerts, or both; and
fast response and fast updates for close cluster aircraft operations.
In accordance with the invention, there is provided a collision avoidance system (CAS), suitable for airborne use on a first aircraft to enable collision avoidance during close proximity operation of a group of CAS equipped aircraft. The system includes a timing device to provide time data, a transmitter to transmit CAS signals at defined send times and in format usable to derive signal transit time values, and a receiver to receive the CAS signals from other aircraft of the group. Also included is a processor coupled to the timing device, transmitter and receiver and responsive to received CAS signals to:
(i) derive received signal parameter values, including signal transit time values representative of differences between send times and receive times of CAS signals received from other aircraft of the group; and
(ii) utilize the signal parameter values to repetitively derive data on range and closing rate between the first aircraft and at least one other aircraft of the group.
Pursuant to the invention, the processor may further be arranged to:
(iii) utilize the data on range and closing rate to derive signals representative of a condition of danger of impending collision between aircraft;
(iv) utilize the data on range and closing rate to repetitively derive 3-D data representative of the three-dimensional relative location of all aircraft of the group;
(v) derive signals representative of evasive action to be taken to remove the first aircraft from a condition of impending collision between aircraft; and
(vi) establish and maintain a local radio sub-net with other aircraft of the group.
Also in accordance with the invention, a method, to operate a collision avoidance system (CAS) within a group of aircraft, includes the steps of:
(a) establishing a local radio sub-net between aircraft of a group of aircraft within a limited volume of airspace;
(b) transmitting aircraft-to-aircraft CAS signals of format usable to derive time reference values;
(c) receiving CAS signals and deriving data on inter-aircraft range and closing rate based on received signal parameter values, including signal transit time between aircraft; and
(d) utilizing data derived in step (c) to derive signals usable to indicate a condition of danger of impending collision between aircraft.
In methods pursuant to the invention, step (c) may include deriving data representative of the three-dimensional location of all aircraft of the group, and step (d) may additionally include deriving signals usable to indicate evasive action to be taken to alleviate a danger of impending collision between aircraft.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.